1. Field of the Invention
The present invention relates to a circuit board and a connection structure of a terminal portion of the circuit board; and particularly relates to a circuit board that is suitably used as a circuit-provided suspension substrate for a hard disk drive, and a connection structure of a terminal portion of the circuit board.
2. Description of Related Art
Generally, a terminal portion for connection with an external terminal formed in an external circuit is formed in a circuit board for use in electronic parts or electronic equipment.
For example, in the circuit-provided suspension substrate, generally, the terminal portion is formed through the steps of: forming a nickel plating layer and a gold plating layer successively, as an underlying plating layer, on a conductor pattern in a specific portion where the terminal portion is to be formed, and forming a soldering bump containing lead and tin on the underlying plating layer.
On the other hand, another gold plating layer is formed as an external terminal in an external circuit such as a read/write substrate to be connected to the circuit-provided suspension substrate.
The above-mentioned circuit-provided suspension substrate and the read/write substrate is designed to be electrically connected with each other if the soldering bump which has been formed in the terminal portion of the circuit-provided suspension substrate is joined by thermocompression bonding to the gold plating layer which has been formed in the external terminal of the read/write substrate.
To improve the connection reliability of the circuit board, it is required to improve the connection strength between the terminal portion of the circuit board and the external terminal of the external circuit from the initial stage of connection. Particularly, because the above-described circuit-provided suspension substrate is used for a hard disk drive, high connection strength from the initial stage of connection is required of the circuit-provided suspension substrate.
Taking the above circumstance into consideration, an object of the present invention is to provide a circuit board which is capable of obtaining high connection strength between a terminal portion of the circuit board and an external terminal of an external circuit from the initial stage of connection so as to improve the connection reliability, and to provide a connection structure of the terminal portion of the circuit board.
In order to achieve the above object, according to the present invention, there is provided a circuit board having a terminal portion for connection with an external terminal formed in an external circuit, the terminal portion including a nickel plating layer and a soldering bump, the nickel plating layer having a thickness within a range of 1.0 to 4.0 xcexcm.
According to the present invention, preferably, the soldering bump contains tin and at least one of silver and copper. More preferably, the soldering bump contains tin, silver and copper.
According to the present invention, the circuit board may be suitably applied to a circuit-provided suspension substrate.
Further, according to the present invention, there is provided a connection structure for connecting a terminal portion of a circuit board with an external terminal formed in an external circuit, the terminal portion including a nickel plating layer and a soldering bump, the nickel plating layer having a thickness within a range of 1.0 to 4.0 xcexcm.